如何在类中初始化const成员变量？ [英] How to initialize const member variable in a class?

问题描述

#include <iostream>

using namespace std;
class T1
{
  const int t = 100;
  public:

  T1()
  {

    cout << "T1 constructor: " << t << endl;
  }
};

当我尝试初始化const成员变量 t 与100。但这给了我以下错误：

When I am trying to initialize the const member variable t with 100. But it's giving me the following error:

test.cpp:21: error: ISO C++ forbids initialization of member ‘t’
test.cpp:21: error: making ‘t’ static

如何初始化 const 值？

推荐答案

const 变量指定变量是否可修改。每次引用变量时将使用分配的常数值。

The const variable specifies whether a variable is modifiable or not. The constant value assigned will be used each time the variable is referenced. The value assigned cannot be modified during program execution.

Bjarne Stroustrup的解释简要地总结一下：

Bjarne Stroustrup's explanation sums it up briefly:

通常在头文件和头文件中声明一个类文件通常包含在许多翻译单元中。但是，为避免复杂的链接器规则，C ++要求每个对象都有唯一的定义。如果C ++允许在类中定义需要作为对象存储在内存中的实体，则该规则将被打破。

A class is typically declared in a header file and a header file is typically included into many translation units. However, to avoid complicated linker rules, C++ requires that every object has a unique definition. That rule would be broken if C++ allowed in-class definition of entities that needed to be stored in memory as objects.

A const 变量必须在类中声明，但不能在其中定义。我们需要在类外定义const变量。

A const variable has to be declared within the class, but it cannot be defined in it. We need to define the const variable outside the class.

T1() : t( 100 ){}

这里的赋值 t = 100 发生在初始化列表中类初始化发生。

Here the assignment t = 100 happens in initializer list, much before the class initilization occurs.

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